Apparatus for slowing down and stopping moving webs or foil

ABSTRACT

Apparatus for controlling the movement of a web comprising a suction table, linkage means connected to said suction table and detector means which actuates said linkage means, said suction table being provided with a normally sealed vacuum reservoir which is opened by operation of said linkage means on actuation of said detector on detection of a fault in said web whereby said vacuum is applied to said web to apply a braking force thereto.

[ Mar. 26, 1974 United States Patent [191 Herzhoff et al.

APPARATUS FOR S LOWING DOWN AND STOPPING MOVING WEBS OR FOIL References Cited UNITED STATES PATENTS inventors: Peter Herzhoff, Leverkusen; Hans Gref, Cologne; Wolfgang Schweicher; Karl Voss, Leverkusen; Oscar 'Peckhaus, Leverkusen; Hans F renken, Leverkusen; Heinrich Bussmann, Opladen, all of Germany Primary ExaminerAllen N. Knowles [73] Assignee: AGFA-Gevaert Aktiengesellschaft, Attorney, Agent, or FirmConnolly and Hutz Leverkusen, Germany Jan. 8, 1973 Appl. No.: 321,977

[57] ABSTRACT Apparatus for controlling the movement of a web 22 Filed:

comprising a suction table, linkage means connected to said suction table and detector means which actu- [30] Foreign Application priority Data ates said linkage means, said suction table being pro- Jan. 13, 1972 vided with a normally sealed vacuum reservoir which German 2201446 y is opened by operation of said linkage means on actuation of said detector on detection of a fault in said web whereby said vacuum is applied to said web to apply a braking force thereto.

, 24, ll 11 Claims, 4 Drawing Figures [58] Field of Search............ 226/39, 95,

PATENTED MR 26 I974 SHEET 1 0F 2 A, m H

A II: VII

FIG. 2

APPARATUS FOR SLOWING DOWN AND STOPPING MOVING WEBS OR FOIL This invention relates to an apparatus for slowing down and stopping webs of foil moving over rollers. The invention is particularly suitable for webs which have been wet coated on one side.

In photographic casting and drying plants, webs of foil which have been wet coated on one side are moved over long series of rollers. If any faults in the photographic layers or if the web breaks, it is important to bring the whole plant to a stop as quickly as possible. Long stopping distances should be avoided because of the resulting waste of material. Moreover, when the web is stopped the wet coated side must not come into contact with any parts of the machinery.

Formerly, when any faults were detected in such photographic casting and drying plants, the plant was simply switched off with an emergency switch. Although this cut off the power supply to the roller drives, the momentum of the web and of the rollers caused the web to run on for a considerable distance. The part of the web in which the fault was situated was then liable to end in an inaccessible part of the plant.

A stopping method has recently been disclosed by which a braking action is also applied to the drives. Although the stopping distance is thereby reduced, it is still not possible to bring the casting and drying plant to a stop so quickly that the fault can be corrected without substantial loss in time and material.

Faults which are particularly important in the production process are tears or. complete rupture of the web. Such faults are particularly likely to occur at the point where the coating is applied, e.g. due to lumps of baryta getting caught in the casting gap.

It is an object of this invention to minimise the loss of time and material. In the event of a fault or tear in the web, the web or more particularly the end of the web must be halted as quickly as possible.

The invention therefore provides an apparatus for controlling the movement of a web comprising a suction table, linkage means connected to said suction table and detector means which actuates said linkage means, said suction table being provided with a normally sealed vacuum reservoir which is opened by operation of said linkage means on actuation of said detector on detection of a fault in said web whereby said vacuum is applied to said web to apply a braking force thereto. Obviously, in the case of a wet coated photographic web, the suction table is brought up to the back surface of the web.

The movement of the suction table to the web is advantageously released by a fault signal. For this purpose the transmission mechanism for shifting the table into the plane of the web is coupled to a fault detection instrument.

The suction table should move as quickly as possible into the plane of the web in response to a fault signal. For this purpose, the transmission mechanism must have a power transmission ratio of at least 2:].

According to a preferred embodiment of the invention while the suction table is being moved into position, its apertures are open to a vacuum chamber which is connected to a vacuum reservoir. The pressure in this vacuum reservoir is maintained at a substantially constant vacuum. The volume of the reservoir is large compared with that of the vacuum chamber so that no changes in pressure occur.

'The friction between the web and the suction table is proportional to the vacuum in the suction table. Another feature of the invention accordingly consists of a measuring device for measuring the vacuum and hence also the friction. In this way, the braking .process becomes measureable.

The braking device desribed above can be used successfully in photographic casting and drying plants. Since tears and separations in the web occur mainly in the casting part of the plant, it is advisable to arrange the braking device adjacent to the casting apparatus.

The major advantage achieved with the invention is that the web can now be stopped much more quickly. Moreover, the friction and hence the braking force can be varied within limits by suitable adjustment of the pressure.

An example of the invention is described in detail below with reference to the drawing in which FIG. 1 shows the arrangement of the suction table in the inoperative position (side view),

FIG. 2 shows the arrangement of the suction table in the operative position (side view) and FIGS. 3 and 4 show the transmission mechanism.

In FIG. 1, the web 1 is passed vertically over rollers 2. The rollers 2 come into contact only with the uncoated back of the web 1. Approximately 25 to 35 mm from the back of the web is the suction table 3, the front surface 4 of which has a plurality of apertures 5. The suction table 3 contains a vacuum chamber 8 sealed by seals 6 and 7. This chamber 8 is connected to a vacuum reservoir (not shown by the pipe 9.) The volume of this reservoir is large compared with the volume of the vacuum chamber 8. The vacuum is produced with a suction pump or ventilator and can be adjusted to any desired value.

In the event of a tear or disruption of the web or a similar fault, a fault detecting device (not shown) issues the instruction for switching off the web drive mechanism. At the same time, the suction table 3 is moved forward into the plane of the web. The back of the web 1 is sucked to the front surface'4 of the suction table 3 and thereby very quickly stopped. The forward position of the suction table 3 is shown in FIG. 2. FIGS. 3 and 4 show the transmission mechanism for shifting the suction table 3 forward into the operative position. The table is supported by the two rocking arms 10 and two lifting arms 1 l. The force for the movement is transmitted by the way of the pneumatic piston 12 and rocking link 13. The forward movement of the suction table 3 stops when the pins 14 of the table 3 bear against the base 15. As the table moves forward, the vacuum chamber 8 is connected to the atmosphere through the now open seal 6 and apertures 5 so that air is sucked through the apertures until the web'l is pressed by suction against the front surface 4, thereby covering the apertures 5. As already mentioned above, the volume of the vacuum reservoir is sufficiently large to ensure that no significant increase in pressure occurs during this time.

The time taken for the braking device to respond is an important parameter. It depends on the nature of the transmission mechanism and the time required for the forward movement of the table. To obtain short response times, the transmission mechanism is so designed that the force transmission ration is greater than 2:1. It has also table found that the time taken for the suction talbe to move forward is considerably reduced by the suction produced. This suction accelerates the suction table 3 in the direction of the web 1. The force of this suction is K F A p, in which P is the total surface area of all the apertures and Ap the differences between atmospheric pressure and the pressure on the suction table. When the suction table 3 has reached the web 1, this force becomes a suction force of equal magnitude by which the web 1 is held to the front surface 4 of the suction table 3. The response time is in practice found to be less than 0.1 second.

The braking force acting on the web 1 is proportional to the negative pressure Ap, the surface area F of the apertures and the friction ,u between the web 1 and front surface 4 of the suction table 3.

The braking force can therefore always be adjusted to the optimum value by suitable choice of the negative pressure Ap even if the friction p. varies.

Example Number of apertures n=566 Diameter of apertures v d=0.8 cm Total surface area of apertures F,=284.3 cm Front surface of suction table 5280 cm Negative pressure in suction box Ap=2000 mm water column A web of foil weighing 85 g/m and running at a velocity of v 60 m/min was braked by means of such a suction table. The braking distance was only cm.

What we claim is:

1. Apparatus for controlling the movement of a web comprising a suction table, linkage means connected to said suction table, actuator means connected to said linkage means for actuating said linkage means, said suction table being provided with a normally sealed vacuum reservoir which is opened by operation of said linkage means on actuation of said actuator means whereby said vacuum is applied to said web to apply a braking force thereto and said linkage means being adapted to move said vacuum table into contact with said web on actuation by said actuator means.

2. Apparatus as claimed in claim 1 in which said linkage means has a power transmission ratio of at least 2:].

3. Apparatus as claimed in claim 1 in which said suction table is provided with a plurality of apertures and with a chamber which is open in both the inoperative and operative positions of the linkage means.

4. Apparatus as claimed in claim 3 which the volume of said chamber is small compared to the volume of said vacuum reservoir.

5. Apparatus as claimed in claim 1 which is provided with means for measuring the vacuum in said suction table.

6. Apparatus as claimed in claim 1, wherein said linkage means comprises a rocking linkage.

7. Apparatus as claimed in claim 1, wherein said actuator means comprises a pneumatic plunger.

8. Apparatus as claimed in claim 1, wherein said suction table comprises an apertured surface, intermediate lugs, a base, seal means between and lugs and said base, slide means connecting said vacuum table to said base whereby said suction table is pennitted to move towards and away from said web, and said seals bing constructed and arranged to seal said apertured surface from said vacuum reservoir when said suction table is disposed remote from said web on said base.

9. Apparatus as claimed in claim 8, wherein said base comprises a pedestal element having a plate element upon a leg, and said seals being provided on said plate element.

10. Apparatus as claimed in claim 9, wherein said suction table comprises a hollow chamber having said apertured surface, an opening in said chamber in a wall remote from apertured surface through which said leg is inserted, said lugs extending within said chamber adjacent said apertured surface and in line with the outside of said plate, a flexible vacuum tight seal between said leg and said opening in said chamber and said seal means being disposed in said periphery of said plate for contacting said lugs when said chamber is disposed remote from said web.

11. Apparatus as claimed in claim 10, wherein stop projections are provided in said chamber adjacent said opening for reacting against the surface of said plate remote from said apertured surface for limiting the travel of said suction table against said web. 

1. Apparatus for controlling the movement of a web comprising a suction table, linkage means connected to said suction table, actuator means connected to said linkage means for actuating said linkage means, said suction table being provided with a normally sealed vacuum reservoir which is opened by operation of said linkage means on actuation of said actuator means whereby said vacuum is applied to said web to apply a braking force thereto and said linkage means being adapted to move said vacuum table into contact with said web on actuation by said actuator means.
 2. Apparatus as claimed in claim 1 in which said linkage means has a power transmission ratio of at least 2:1.
 3. Apparatus as claimed in claim 1 in which said suction table is provided with a plurality of apertures and with a chamber which is open in both the inoperative and operative positions of the linkage means.
 4. Apparatus as claimed in claim 3 which the volume of said chamber is small compared to the volume of said vacuum reservoir.
 5. Apparatus as claimed in claim 1 which is provided with means for measuring the vacuum in said suction table.
 6. Apparatus as claimed in claim 1, wherein said linkage means comprises a rocking linkage.
 7. Apparatus as claimed in claim 1, wherein said actuator means comprises a pneumatic plunger.
 8. Apparatus as claimed in claim 1, wherein said suction table comprises an apertured surface, intermediate lugs, a base, seal means between and lugs and said base, slide means connecting said vacuum table to said base whereby said suction table is permitted to move towards and away from said web, and said seals bing constructed and arranged to seal said apertured surface from said vacuum reservoir when said suction table is disposed remote from said web on said base.
 9. Apparatus as claimed in claim 8, wherein said base comprises a pedestal element having a plate element upon a leg, and said seals being provided on said plate element.
 10. Apparatus as claimed in claim 9, wherein said suction table comprises a hollow chamber having said apertured surface, an opening in said chamber in a wall remote from apertured surface through which said leg is inserted, said lugs extending within said chamber adjacent said apertured surface and in line with the outside of said plate, a flexible vacuum tight seal between said leg and said opening in said chamber and said seAl means being disposed in said periphery of said plate for contacting said lugs when said chamber is disposed remote from said web.
 11. Apparatus as claimed in claim 10, wherein stop projections are provided in said chamber adjacent said opening for reacting against the surface of said plate remote from said apertured surface for limiting the travel of said suction table against said web. 